Phetch is a game with a purpose intended to label images on the internet with descriptive captions suitable to assist sight impaired readers.
Approximately 75% of the images on the web do not have proper ALT text labels, making them inaccessible through screen readers.
Phetch was created by Luis von Ahn and Shiry Ginosar of Carnegie Mellon University following the pattern set by the earlier ESP game.
The data produced as the side effect of playing the game is the describer's descriptions of the image.
An imagined system for serving these descriptions from a centralized server is described in the Phetch paper.